Tanning apparatuses such as booths and beds represent a popular and growing industry estimated at $7 billion as of 2003. A major component of tanning apparatuses is the fluorescent lamp used to deliver ultraviolet (“UV”) radiation to a user. Other types of lamps used in related applications include high pressure lamps, facial lamps, and quartz high pressure lamps. Such lamps mimic the effects of the sun to effectively tan the skin of a user by delivering a combination of UVA and UVB radiation while filtering out UVC, the most harmful UV radiation emitted by the sun. All fluorescent lamps share the same basic design: a glass tube lined with a coating of phosphors, electrodes on the inside, and end caps at each end to seal the lamp. The tube contains mercury vapor gas under low pressure, which is ionized upon exposure to an electric current. UV emissions result from the energy transfer between electrons in a supplied current and the mercury gas atoms. The most prevalent lamps in the tanning industry generally exceed the natural intensity of the sun by two to five times.
Tanning lamps are characterized by a useful lifetime in which they deliver an effective dose of ultraviolet radiation while remaining within the safe voltage range specified by the tanning apparatus or lamp manufacturer. Commercially available fluorescent lamps intended for use in tanning apparatuses are typically quoted to have a useful lifetime as long as 1000 hours or more. In practice, however, it is not uncommon for lamps to last for only a percentage of advertised lifetime. One of the reasons for this limitation is that lamps are often operated at a relatively high voltage to ensure that UV emission is sufficient to ensure an effective result to the user. High voltages can raise the operating temperature of the lamp, thereby shortening lamp life.
Some users employ voltage transformers known as “buck boosters” to bring their tanning apparatuses within specified voltage ratings. A buck booster will either increase or decrease the incoming voltage so it will be at a level that the tanning apparatus was designed to utilize. Buck boosters operate as step transformers such that they are only able to increase or decrease the incoming voltage by a pre-set number of volts, or by a pre-set percentage of incoming voltage. For example, common buck boosters are sold in a +/−16/32 or +/−12/24 configuration, meaning that they can increase or decrease voltage 16 or 32 volts or 12 or 24 volts, respectively. These units are used without regard to the UV delivery efficiency of the lamps used in a tanning apparatus, but rather are used to simply bring the operating voltage to within manufacturer specifications.
The inventor has recognized that conventional tanning apparatuses and related operation methods are inefficient. The use of unnecessarily high operating voltages to maximize the delivered UV dose results in a drastic decrease in lamp life. The use of buck boosters is inefficient because they impose an arbitrary step in voltage without regard to UV dose. Moreover, regardless of whether a buck booster is used, conventional tanning apparatus operating methods make use of a static voltage throughout the life of a tanning lamp. If this single voltage is too high, lamp life can be compromised; if too low, efficient tanning results will not be obtained.
Recognizing the shortcomings of conventional tanning apparatuses and operating methods, there is a need for efficient and cost effective apparatuses and methods in which operating voltage is precisely and dynamically controlled for enhanced operating efficiencies. Relatedly, there is a need to control the output of tanning lamps so that it is generally constant over the lamp lifetime.